According to a configuration shown in FIG. 21, for example, a wheel 1 constituting a wheel of a car and a rotor 2 constituting a disc brake as a braking system are supported rotatably on a knuckle 3 constituting a suspension system. More particularly, an outer ring 6 as a stationary ring, which constitutes a wheel bearing unit 5, is fitted into a circular bearing hole 4 formed in the knuckle 3 and then fixed by a plurality of bolts 7. Meanwhile, the wheel 1 and the rotor 2 are coupled/fixed to a hub 8, which constitutes the wheel bearing unit 5, by a plurality of studs 9 and nuts 10.
Double row outer ring raceways 11a, 11b serving as a stationary raceway respectively are formed on an inner peripheral surface as a stationary peripheral surface of the outer ring 6, and a stationary flange 12 is formed on an-outer peripheral surface. Such outer ring 6 is fixed to the knuckle 3 by coupling the stationary flange 12 to the knuckle 3 via the bolts 7.
In contrast, a rotary flange 13 is formed on a part of an outer peripheral surface of the hub 8, which is projected from an outer end opening of the outer ring 6 (Here, the outside in the axial direction means the outside portion in the width direction in a fitted state to a car, and corresponds to the left side in respective FIGS. except FIGS. 2 3, 6, 7, 9, 18. In contrast, the right side in respective FIGS. except FIGS. 2 3, 6, 7, 9, 18, which is located on the center side in the width direction in a fitted state to a car, is defined as the inside in the axial direction). The wheel 1 and the rotor 2 are coupled/fixed to one side surface (an outer side surface in an illustrated example) of the rotary flange 13 by the studs 9 and nuts 10. Also, an inner ring raceway 14a as the rotary raceway is formed on a middle portion of an outer peripheral surface of the hub 8 to oppose to the outside outer ring raceway 11a out of the double row outer ring raceways 11a, 11b. Then, an inner ring 16 constituting a rotating member 23 as a rotary ring together with the hub 8 is fitted onto a small-diameter stepped portion 15 that is formed on an outer peripheral surface of an inner end portion of the hub 8. Then, an inner ring raceway 14b is formed on an outer peripheral surface of the inner ring 16 as the rotary raceway to oppose to the inside outer ring raceway 11b out of the double row outer ring raceways 11a, 11b. Here, the outer peripheral surfaces of the hub 8 and the inner ring 16 correspond to a rotary peripheral surface set forth in claims.
A plurality of balls 17, 17 serving as a rolling element respectively are provided rollably between the outer ring raceways 11a, 11b and the inner ring raceways 14a, 14b in a state that these balls are held by cages 18, 18 respectively. According to this configuration, a double row angular contact ball bearing can be constructed in a back-to-back arrangement style, and thus the rotating member 23 is borne rotatably on the inside of the outer ring 6 to support the radial load and the thrust load. Then, seal rings 19a, 19b for isolating an internal space 26, in which the balls 17, 17 are provided, from the outside are provided between inner peripheral surfaces of both end portions of the outer ring 6 and the outer peripheral surface of the middle portion of the hub 8 and the outer peripheral surface of the inner end portion of the inner ring 16 respectively. Then, since an illustrated example gives the wheel bearing unit 5 that supports the driven wheel (the rear wheel of the FR car and the RR car, the front wheel of the FF car, all wheels of the 4WD car), a spline hole 20 is formed in the center portion of the hub 8. Then, a spline shaft 22 of a constant velocity joint 21 is inserted into this spline hole 20.
In using such wheel bearing unit 5, as shown in FIG. 21, the outer ring 6 is fixed to the knuckle 3 and also the wheel 1, on which a tire (not shown) is fitted, and the rotor 5 are fixed to the rotary flange 13 of the hub 8. Also, a combination of the rotor 2 and a support member and a caliper (both not shown) fixed to the knuckle 3 constitutes the braking disc brake. In the braking operation, a pair of pads that are provided to put the rotor 2 therebetween are pushed against both side surfaces of the rotor 2 serving as braking friction surfaces. Here, in this specification, the braking friction surface signifies a side surface of the rotor in the axial direction when the braking rotation body is composed of the rotor, while the braking friction surface signifies an inner peripheral surface of the drum when the braking rotation body is composed of the drum.
Meanwhile, it is known that the vibration called the shudder that entails an unpleasant noise is often generated in the braking operation of the car. As the cause of such vibration, various factors such as an uneven friction condition between a side surface of the rotor 2 and a lining of the pad, and the like are known. Also, it is known that the run-out of the rotor 2 acts as the major cause. In other words, the side surface of the rotor 2 must be set essentially at a right angle to a center of rotation of the rotor 2, nevertheless it is difficult to make a complete right angle due to the inevitable manufacturing error, and so on. As a result, it is inevitable that, though its amount is quite small, the side surface of the rotor 2 swings in the rotating shaft direction (the lateral direction in FIG. 21) during the running of the car. In case such swing (an amount of displacement in the lateral direction in FIG. 21) is increased, the shudder is caused when the linings of a pair of pads are thrust against both side surfaces of the rotor 2 to brake. Also, in case the drum constituting the drum brake is fixed to the side surface of the rotary flange 13, the vibration like the shudder is also caused when the brake shoes are pushed against the inner peripheral surface in the situation that this inner peripheral surface of the drum is not completely parallel with a center of rotation of the drum.
In order to suppress the shudder generated due to such causes, it is important to suppress (improve) the swing of the side surface of the rotor 2 in the axial direction (axial swing) or the swing of the inner peripheral surface of the drum in the radial direction. For example, in Patent Literatures 1, 2, a method of manufacturing the wheel bearing unit that takes account of the swing of the braking friction surface of the braking rotation body such as the rotor 2, or the like is set forth. In the case of the method of manufacturing the wheel bearing unit set forth in Patent Literature 1, when one side surface of the rotary flange provided to the outer peripheral surface of the hub is processed into predetermined shape and dimension, first respective constituent members of the wheel bearing unit including the hub whose one side surface is not processed yet are assembled. Then, while rotating the hub by the spindle that is inserted into the inside of the hub in the situation that the end portion of the outer ring is clamped by the chuck of the processing machine, one side surface of the rotary flange provided to the outer peripheral surface of this hub is finished to the predetermined shape and dimension by putting the grinding tool onto this one side surface. In the case where the wheel bearing unit is manufactured by such method, a perpendicularity of one side surface of the rotary flange to a center of rotation of the hub can be improved irrespective of a dimensional error or an assembling error that is inevitable in manufacturing respective constituent members. Thus, the swing of the braking friction surface of the braking rotation body such as the rotor, or the like fixed to this one side surface can be suppressed to some extent.
Also, in the case of the method of manufacturing the wheel bearing unit set forth in Patent Literature 2, the hub is rotated by the spindle that is inserted into the inside of this hub in the situation that the rotor is fixed to one side surface of the rotary flange provided to the outer peripheral surface of the hub. Then, while rotating the hub, respective portions are finished into predetermined shape and dimension by putting the cutting tool onto both side surfaces of the rotor and a portion of the outer peripheral surface of the hub, onto which the inner ring is fitted. In the case where the wheel bearing unit is manufactured by such method, a perpendicularity of the braking friction surface provided to both side surfaces of the rotor to a center of rotation of the hub can be improved regardless of the dimensional error or the assembling error that is inevitable in manufacturing respective constituent members. Thus, the swing of this rotor can be suppressed to some extent. In this case, as the prior art literatures that are associated with the present invention, there exist Patent Literatures 3 to 8 in addition to above Patent Literatures 1, 2.
[Patent Literature 1]
U.S. Pat. No. 6,415,508 Specification
[Patent Literature 2]
U.S. Pat. No. 5,842,388 Specification
[Patent Literature 3]
JP-A-2000-227132 Gazette
[Patent Literature 4]
JP-A-2001-318105 Gazette
[Patent Literature 5]
JP-A-11-83881 Gazette
[Patent Literature 6]
U.S. Pat. No. 6,364,426 Specification
[Patent Literature 7]
U.S. Pat. No. 6,071,180 Specification
[Patent Literature 8]
U.S. patent application Publication No. 2002/0066185
Specification
In recent years, in order to get a rotation speed signal used to operate the anti-lock brake system (ABS) or the traction control system (TCS), the rotation speed sensing device is incorporated into the above wheel bearing unit. For example, in the configuration shown in FIG. 21, in some case an encoder consisting of a permanent magnet is fitted/fixed onto an end portion of the inner ring 16 rotated together with the wheel, and also a rotation speed sensor is fitted to either the outer ring 6 or a part of the member such as the knuckle 3, or the like fixed to this outer ring 6 such that a sensing portion of the sensor opposes to a sensed portion of the encoder. In such configuration, from a viewpoint of assuring a sensing performance (reliability) of the rotation speed sensor, it is necessary to prevent the foreign matter such as a magnetic powder, or the like from adhering the sensed portion of the encoder. In contrast, in the case of the method of manufacturing the wheel bearing unit set forth in above Patent Literatures 1, 2, it is not considered at all that the encoder is fixed to the hub constituting the rotating member or the inner ring. For this reason, a following disadvantage {circle around (1)} is caused when the encoder is provided to the wheel bearing unit set forth in above Patent Literatures 1, 2.
{circle around (1)} Upon grinding or cutting either one side surface of the rotary flange or the braking friction surface of the braking rotation body such as the rotor, or the like couple/fixed to this one side surface to improve a perpendicularity of the braking friction surface of the rotor to the center of rotation of the hub, it is possible that chips as the magnetic material generated by this grinding or cutting adhere to the sensed portion of the encoder. In case the chips adhere in this manner, a sensing performance of the rotation speed sensor becomes worse in the wheel bearing unit into which the rotation speed sensing device is incorporated.
Also, in the case of the method of manufacturing the wheel bearing unit set forth in above Patent Literatures 1, 2, a following disadvantage {circle around (2)} is present respectively.
{circle around (2)} First, in the case of the configuration set forth in above Patent Literature 1, there exists the dimensional error or the assembling error that is inevitable in manufacturing between the side surface of the rotary flange provided to the outer peripheral surface of the hub and the side surface of the braking rotation body such as the rotor, or then like fixed to this side surface. Therefore, it is difficult to say that the swing of the braking friction surface of the braking rotation body can be suppressed satisfactorily. Then, in the case of the method of manufacturing the wheel bearing unit set forth in above Patent Literature 2, there exists the dimensional error or the assembling error that is inevitable in manufacturing a plurality of parts that are located between the knuckle constituting the suspension system and the portion, on which the inner ring is fitted, of the outer peripheral surface of the hub. Therefore, it is also difficult to say that the swing of the side surface of the braking rotation body can be suppressed satisfactorily. Here, in Patent Literature 3, the measure to regulate a degree of instability of the side surface of the rotor fixed to the rotary flange, which is provided to the outer peripheral surface of the hub, while the hub constituting the wheel bearing unit is rotated around the outer ring is set forth. However, in this Patent Literature 3, a method of manufacturing the wheel bearing unit in which a degree of instability of the side surface is regulated is not set forth at all.